1. Field of the Invention
The present invention relates to a hearing protective earplug according to the preamble of claim 1 and to a corresponding manufacturing method.
2. Description of Related Art
A large part of the population is exposed to hazardous noise from time to time. This can be at work, whilst traveling, during leisure activities or at home. The exposure can lead to permanent hearing loss, distract people's attention from other hazards or simply cause stress. In order to prevent both accidents and permanent hearing damage, hearing protection devices (HPDs) have been provided in many styles and over many years. It started with the earmuff which is still very relevant and addresses very noisy environments (e.g. airports, construction, shooting) or complex working/communication situations (e.g. fighter pilots). Over the years development of biocompatible soft materials has enabled soft earplugs in different styles and colors as well as recent development of “one fits many” standard semi-soft earplugs in silicon-rubber type materials. For severe situations even the combination of an earmuff and an “in-the-ear” HPD is required to achieve desired attenuation. The physical limitation of hearing protection based on ear worn devices is defined where bone-conduction (body acoustics) becomes dominant at around 40 dB attenuation.
A common disadvantage of the above mentioned HPD styles is wearing discomfort. In case of the earmuffs, they are large which creates difficulties in combination with other head worn gear and they “close off” the ear too much for most applications. The in-the-ear styles mentioned are devices made to fit “the average” ear in one way or the other. Either the fit is provided by softness of the material which leads to undefined device insertion and undefined attenuation, or the fit is provided by standard shaped structures intended to block off the ear canal. In both cases the flat distribution of the individual shape of the outer ear and the ear canal leads to bad fit, pressure points in the ear and undefined positioning of the device.
To address this wearing comfort issue, in-the-ear hearing aid technology has been applied making customized ear molds with passive acoustical filter. These are long lasting devices with good wearing comfort. However, this customization process is traditionally a very manual process creating varying results over time, low reproducibility and the quality is very operator skill dependent.
The idea to use rapid prototyping technology, such as layer-by-layer laser sintering, in manufacturing shells, primarily for hearing aids, is described, for example, in U.S. Pat. No. 6,533,062 B1 or U.S. 2003/0133583 A1.
Environmental sounds are typically comprised of a mixture of various sound wave frequencies having varying intensities. It is well documented that repeated or prolonged exposure to sounds of sufficiently high sound pressure level will cause temporary or permanent hearing loss, i.e. can damage the auditory organ and cause serious hearing problems, including deafness. Harmful noise such as caused by explosions or bursts are often comprised of a mixture of sound wave frequencies of varying intensity. These disturbing frequencies are in both the high and low frequency bands and have an intensity sufficient to cause hearing problems. Individuals who are frequently exposed to such disturbing and sometimes dangerous frequencies and intensities run the risk of incurring such injuries as hearing loss or even deafness. These individuals include workers at demolition or construction sites, operators of heavy, noisy equipment and those in active military service. Ear (i.e. hearing) protection is needed to prevent a loss in hearing acuity and the gradual increase in the threshold of hearing resulting from extended exposures to loud noise.
In general, higher sound attenuation of a hearing protection device will reduce the communication ability with the surroundings. The attempts of the prior art to solve this problem, namely to configure the frequency selective sound attenuation such as to retain a high dynamic in speech or voice frequencies, have failed because of the stringent requirements set up by the high noise concentration at certain working places and in the military area, for example, and the worker, employee or soldier must remove the hearing protection device if he wants to hear a person who wants to communicate with him.
Furthermore, personal communication in high noise fields is a major problem for wearers of HPDs when they are occupied in environments with changing sound or noise amplitude. In such situations, it is highly desired to adapt the hearing protection to the actual noise in terms of amplitude, not primarily in terms of noise frequency. In these cases, the user should change his hearing protection device against another one with higher or lower damping ability. This is complicated since there is a necessity to store a number of different HPDs. Moreover, these different HPDs must not only be provided as such but also, due to hygienic reasons, this number of different HPDs must be provided separately for each person to be admitted to the noisy area concerned.
U.S. Pat. No. 6,148,821 discloses a selective non-linear attenuating earplug according to the preamble of claim 1, in which the button comprises a hollow stem which is inserted into a mating cylindrical outer opening of the shell. The hollow stem and the cylindrical wall of the outer opening of the shell both have a radially extending hole, which may be aligned by rotating the stem relative to the shell. The distal end of the hollow stem is provided with a sound attenuation filter connecting the interior of the hollow stem with a sound bore within said shell communicating with the user's ear canal. When the two holes are aligned, sound may enter through the opening into the interior of the hollow stem, pass through the filter and reach, attenuated by the filter, the ear canal.
However, this approach does not allow non-attenuated sound communication and lacks convenient and safe operation by the user, since the button has to be reset manually and the button has to be rotated.
It is an object of the invention to provide for a hearing protection earplug which is operable to provide temporarily for a full sound communication and which is convenient and safe to handle. It is a further object to provide for a corresponding manufacturing method.